ANSI/IEEE standards regulate the accepted dimensions, for example, length by depth, of the electronic circuit cards utilized in conjunction with standard communications backplanes. Circuit cards are generally provided in certain lengths that are often directly related to the number of backplane connectors attached to a bottom edge of the card. For example, a circuit card of length 3U typically has one backplane connector mounted on its bottom edge. Cards of lengths 6U and 9U also have at least one backplane connector and often have two and three backplane connectors, respectively, mounted on their bottom edges. These connectors mate with corresponding connectors mounted to the backplane and thus electrically connect the card to the backplane and enable communications therebetween. Other standard and non-standard card lengths are commercially available.
Circuit cards are also provided in a number of standard depths. Two of the most popular depths are 160 mm and 220 mm. Other card depths, both shorter and taller than the standard depths recited above, are commercially available.
A circuit card is typically installed within an enclosure or chassis by positioning the card between a pair of card guides mounted at the opposite ends of each slot location. Each card guide includes a guide slot that accepts and retains one of the side edges of the installed card. As the card is inserted down the guide slot, each connector on the bottom edge of the card is inserted into a mating connector on the backplane. Installation of the circuit card is completed by retaining the top edge of the card within the enclosure to prevent shifting of the card along the guide slot and disengagement of the card connectors mated to the backplane connectors.
The card enclosures or chassis of the prior art includes card guides that only accommodate one depth of circuit card per slot location. The prior art chassis is further designed with one or more fixed partitions to segregate areas for accommodating only one type or dimension of circuit card. For example, each individual area only accepts cards having a predetermined length by depth. The use of partitions in the prior art chassis fixes the number of slot locations available for accepting cards of each predetermined dimension. Thus, within the enclosure or chassis of the prior art, certain areas are inflexibly dedicated to receive a predetermined number of circuit cards having only one particular dimension.
The most significant disadvantage experienced with the prior art enclosure or chassis design and card guide mounting system is its limited ability to expand or adapt to accept additional replacement or modified circuit cards. This limitation is primarily caused by the use of segregated or partitioned areas dedicated to receive a fixed number of cards having a fixed dimension. Once an area was full, additional cards can not be accommodated. The inability to adapt to or accommodate different numbers of circuit cards having different dimensions severely limits the life span of the enclosure or chassis because circuit redesigns often necessitate substantial modification and often complete replacement of the chassis in order to accept new cards of differing numbers and sizes.
Accordingly, there is a need for a chassis and card mounting system capable of accepting for installation cards of varying standard dimensions regardless of location. With such a system, modifications or redesigns of individual or entire systems of circuit cards may be implemented without additionally requiring that the enclosure or chassis be redesigned or replaced.